CN102981390B - Apparatus for the exact reconstruction of the object wave in off-axis digital holography - Google Patents

Apparatus for the exact reconstruction of the object wave in off-axis digital holography Download PDF

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CN102981390B
CN102981390B CN201210311755.4A CN201210311755A CN102981390B CN 102981390 B CN102981390 B CN 102981390B CN 201210311755 A CN201210311755 A CN 201210311755A CN 102981390 B CN102981390 B CN 102981390B
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energy level
reference beam
image energy
image
optical
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CN102981390A (en
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K-N.赵
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Mitutoyo Corp
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/08—Synthesising holograms, i.e. holograms synthesized from objects or objects from holograms
    • G03H1/0866—Digital holographic imaging, i.e. synthesizing holobjects from holograms
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/16—Processes or apparatus for producing holograms using Fourier transform
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02015—Interferometers characterised by the beam path configuration
    • G01B9/02027—Two or more interferometric channels or interferometers
    • G01B9/02028—Two or more reference or object arms in one interferometer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02015—Interferometers characterised by the beam path configuration
    • G01B9/02032—Interferometers characterised by the beam path configuration generating a spatial carrier frequency, e.g. by creating lateral or angular offset between reference and object beam
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02041—Interferometers characterised by particular imaging or detection techniques
    • G01B9/02047—Interferometers characterised by particular imaging or detection techniques using digital holographic imaging, e.g. lensless phase imaging without hologram in the reference path
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/0209—Low-coherence interferometers
    • G01B9/02091—Tomographic interferometers, e.g. based on optical coherence
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/0443—Digital holography, i.e. recording holograms with digital recording means
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/26—Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique
    • G03H1/2645—Multiplexing processes, e.g. aperture, shift, or wavefront multiplexing
    • G03H1/265—Angle multiplexing; Multichannel holograms
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/10—Processes or apparatus for producing holograms using modulated reference beam
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/26—Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique
    • G03H1/28—Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique superimposed holograms only
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/0443—Digital holography, i.e. recording holograms with digital recording means
    • G03H2001/0452—Digital holography, i.e. recording holograms with digital recording means arranged to record an image of the object
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/0443—Digital holography, i.e. recording holograms with digital recording means
    • G03H2001/0454—Arrangement for recovering hologram complex amplitude
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/0443—Digital holography, i.e. recording holograms with digital recording means
    • G03H2001/0454—Arrangement for recovering hologram complex amplitude
    • G03H2001/0456—Spatial heterodyne, i.e. filtering a Fourier transform of the off-axis record
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/08—Synthesising holograms, i.e. holograms synthesized from objects or objects from holograms
    • G03H1/0808—Methods of numerical synthesis, e.g. coherent ray tracing [CRT], diffraction specific
    • G03H2001/0825—Numerical processing in hologram space, e.g. combination of the CGH [computer generated hologram] with a numerical optical element
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/08—Synthesising holograms, i.e. holograms synthesized from objects or objects from holograms
    • G03H1/0866—Digital holographic imaging, i.e. synthesizing holobjects from holograms
    • G03H2001/0883—Reconstruction aspect, e.g. numerical focusing
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2222/00—Light sources or light beam properties
    • G03H2222/20—Coherence of the light source
    • G03H2222/24—Low coherence light normally not allowing valuable record or reconstruction
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2223/00—Optical components
    • G03H2223/26—Means providing optical delay, e.g. for path length matching
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06E—OPTICAL COMPUTING DEVICES; COMPUTING DEVICES USING OTHER RADIATIONS WITH SIMILAR PROPERTIES
    • G06E3/00—Devices not provided for in group G06E1/00, e.g. for processing analogue or hybrid data
    • G06E3/001—Analogue devices in which mathematical operations are carried out with the aid of optical or electro-optical elements
    • G06E3/003—Analogue devices in which mathematical operations are carried out with the aid of optical or electro-optical elements forming integrals of products, e.g. Fourier integrals, Laplace integrals, correlation integrals; for analysis or synthesis of functions using orthogonal functions

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • General Health & Medical Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Engineering & Computer Science (AREA)
  • Computing Systems (AREA)
  • Health & Medical Sciences (AREA)
  • Mathematical Physics (AREA)
  • Holo Graphy (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

The invention provides a method and an apparatus for preparing a digital hologram representing an object, comprising generating a measurement beam and two reference beams, irradiating the object by the measurement beam and guiding the reflected measurement beam to an optical sensor, guiding the reference beams to mirror means extending under a slanting angle and guiding the reflected beams to the sensor to make the beams generate an interference pattern on the sensor, providing a digital signal representing the pattern on the sensor, processing the signal to obtain a digital hologram, subjecting the digital hologram to a Fourier transform in the spatial frequency domain to obtain a spectrum comprising a DC-term, two image terms, and two conjugate image terms, filtering the spectrum to obtain a term representing the object and replacing a section of an image term overlapped by the DC-term by the corresponding section of the other image term.

Description

To the device of the accurate reconstruction of object wave in the outer hologram of axle
Technical field
The present invention relates in order to real-time 3D measurements are using the amplitude of the digital holography of digital holographic microscopy and determine Amount phase imaging.
Background technology
Digital holography be for not only record amplitude image picture and also record phase image with normal imaging technology Relative effective tool.The major advantage of digital holography obviously stems from only to be surveyed with single image to the real-time 3D of target Amount.In addition, even if sample is not at pinpointed focus or when optical system includes aberration of light (aberration), digital hologram shines Physiognomy also allows the amplitude and phase place of reconstruction of objects ripple (object wave).
Based on these advantages, recently, digital holography has been widely used in industry and scientific domain, especially should The amplitude of active somatic cell and the biomedical sector of phase image are monitored in real time.In process industry product, digital holography Art can significantly improve volume of production to the real-time inspection of product using in profile and tomography ground.
The principle of digital holography starts from based on two step process, record and the conventional photographic photography for reconstructing. In record process, the scattered wave from object is interferenceed with reference wave, and interference figure is recorded in light-sensitive medium, i.e., It produces " hologram ".After record process, by irradiating hologram rather than object with identical reference wave thing is carried out The reconstruct of bulk wave.
Similar, digital holography also has and conventional photographic photography identical process, but it is using taking the photograph Camera or optical pickocff are used as recording medium.Additionally, digital hologram allows digital (numerical) image reconstruction, its In virtually analog physical reconstruct ripple, and object wave can be recovered by digital wave propagation.
According to the alignment between optical arrangement, i.e. reference wave and measurement ripple, digital holography (DH) generally can be by It is categorized as axle outer DH and (in-line) DH that is in line.In order to avoid the DC energy level Chong Die with object wave energy level (term), (zeroth order is spread out Penetrate) and paired image energy level (conjugation of object wave), the outer DH of axle is used has angle of inclination between reference wave and measurement ripple Spatial modulation and space filtering technology.Take to eliminate the work of those influence of noises without the DH that is in line, the outer DH of axle permits Perhaps from the amplitude and phase image of hologram reconstruction sample.
On the other hand, the DH that is in line is usually taken the other technologies of such as phase offset only to extract object from hologram Ripple.Inherently, the DH that is in line loses the main power of such as real-time measurement capability in the application, although being in line DH permissions Clearly reconstructed image.Recently, in order to overcome this to limit, it has been suggested that the parallel light path length based on space phase offset device Skew DH is used for measurement in real time.But, the method is limited by the available pixel quantity in CCD camera or optical pickocff System.
In outer (off-axis) DH of axle in industry and scientific domain is most widely used for, caused by the inclination of reference mirror The spatial modulation of image is introduced in digital hologram, as shown in figure 1, and its be used to extract object wave in spatial frequency domain Filtering Processing.Configuration shown in Fig. 1 includes light source 1, such as divides as LASER Light Source, beam splitter 3, positioned at light source 1 and light beam Collecting lenses 2, reference mirror 5, the first object lens 4, imaging len 6, optical pickocff 7, the second object lens 8 and sample between device 3 Retainer 9.
Light source 1 launches the first reference beam 10, and it passes through collecting lenses 2, beam splitter 3, the first object lens 4, reference mirror 5, it is launched at reference mirror 5, again passes through the first object lens 4, beam splitter 3, and reference beam is inclined at beam splitter 3 Imaging len 6 is gone to, and it runs into optical pickocff 7.
Additionally, the emission measurement light beam 11 of light source 1, it passes through collecting lenses 2, is deflected by beam splitter 3, through the second thing Mirror 8, runs into sample 9, is reflected by sample 9, again passes through the second object lens 8, beam splitter 3, imaging len 6, eventually encounters biography Sensor 7 together with the first reference beam 10 forming interference figure.
The major advantage of configuration is and digital holography and the phase offset digital holography of being such as in line outside axle The other configurations of art using single hologram conversely, obtain object wave.Obtained comprising interference fringe by the outer geometry of axle After digital hologram, the two-dimension spectrum of hologram can be obtained by the Fourier transform in spatial frequency domain, wherein dry The different energy levels for relating to contribute to good separation.The spectral representation of the DC energy levels of the spectrum being plotted as in the center of Fig. 5 A The spectrum of the intensity of reference wave and object wave (not interfering energy level).
The spatial frequency of interference energy level orientates the centrosymmetry with regard to image as.It depends on incidence to incline to the distance at center Oblique angle, its must it is sufficiently large with guarantee DC energy levels and those interfere energy levels be kept completely separate.Then can in spatial frequency domain mistake Undesired energy level is filtered, and can only extract and obtain object wave, although in spite of using high resolution camera, space Frequency is all restricted.After the filtering, by the way that object is obtained to the digital reconstruction of hologram as reference wave using plane wave Amplitude and phase image.
More specifically, the method that prior art discloses the digital hologram for preparing the image for representing object, the method bag Include step：Coherent measurement light beam and the first coherent reference light beam are produced by light source；Object and will be by is irradiated by measuring beam The measuring beam of object reflection is directed to optical pickocff；First reference beam is directed in the light for the first reference beam Axle extends below the first mirror with the angle different from 90 °, and will be directed to optics by the first reference beam that the first mirror reflects Sensor so that measuring beam and the first reference beam produce on a sensor together interference figure；Read optical pickocff simultaneously The digital signal for representing the interference figure for producing on the optical sensor is provided；Process the digital signal to obtain digital hologram Figure；Make the Fourier transform in digital hologram experience spatial frequency domain with obtain including DC energy levels, the first image energy level and The two-dimension spectrum of the first conjugated image energy level；And the spectrum experience filtering for making to obtain is to obtain the energy level for representing object.
Most important process is that elimination other energy levels, i.e. DC energy levels (zeroth order) and paired image energy level are (common in the outer DH of axle Yoke ripple) and obtain the space filtering process of high-quality object wave from digital hologram.
T.M.Kreis describes straightforward procedure (T.M.Kreis the and W.P.P.J ü for suppressing DC energy levels from hologram Ptner, " Suppression of the dc term in digital holography " (" suppresses in digital hologram Dc energy levels "), Opt.Eng.36,2357-2360,1997).The method is that mean intensity is deducted from digital hologram, this Allow only to eliminate so-called DC energy levels from the image of reconstruct.It is the plain mode that DC energy levels are reduced from hologram, but It is in most of the cases inadequate.For example, if generally object intensity of wave is not constant in holographic plan, use The method can not eliminate the DC energy levels that object wave causes.
E.Cuche proposes the improved method (E.Cuche for being known as space filtering used in the form of band filter Et al., " Spatial filtering for zero-order and twin-image elimination in digital Off-axis holography " (for the space filtering that the zeroth order and paired image in the outer hologram of digital axle is eliminated), Appl.Opt.39 (23), 4070-4075,2000).
The U.S. Patent number US6262818 of Cuche et al. describes the spatial filtering method of two ways；A kind of conduct makes Band-pass filtering method with FFT in spatial frequency domain, another kind of optical space filtering method as based on 4-f systems.This It is false that a little methods depend on DC energy levels and desired energy level to be separated the key allowed to by filtering suppression DC energy levels well If.But, they are also limited by these two aspects；One be a certain ratio spectrum can be it is available, another be space filter Ripple generally needs manpower intervention to select desired rank.
Disclose in the U.S. Patent number US6809845 of Kim et al. and realize the another of effective percentage ripple using other image One method.In this method, in addition to the hologram in system, also obtain with reference to intensity of wave and object intensity of wave, these use In the DC energy levels that hologram is removed by simple subtraction.
But it needs the other hardware of such as beam blocker (beam blocker), and should record except complete Two more images outside breath figure.In this case it is assumed that environmental condition and systematic parameter should keep constant.
Recently, nonlinear reconstruction technology (N.Pavillon et al., " Suppression of the are had been introduced into Zero-order in off-axis digital holography through nonlinear filtering " are (by non- The suppression of the zeroth order in the countershaft outer digital hologram of linear filtering), Appl.Opt.48 (34), H186-H195,2009).Its Realization is enabled accurate without zeroth order reconstruct in the outer DHM of axle, even if zeroth order and object wave spectra overlapping.Nonlinear filtering technique exists To work under two actual hypothesis of digital hologram；First, the spectrum of object wave should be restricted to the quadrant of Fourier domain, Second, the intensity of object wave should be more much smaller than reference wave.
But, the object wave of small intensity may reduce the observability of interference fringe and even reduce signal to noise ratio (SNR), and this can Other mistakes can be caused.The effectiveness that this means the method is in actual applications limited.
On the other hand, the information obtained during disclosing by adopting wavefront reconstruction in an iterative process suppresses zeroth order energy Level (N.Pavillon et al., " Iterative method for zero-order suppression in off-axis Digital holography " (" alternative manner that the zeroth order in the outer digital hologram of axle suppresses "), Opt.Express 18 (15), 15318-15331,2010).So as to, allow to realize DC energy levels suppress and without knowing with regard to any existing of object Know.
But, this technology spending calculates the time, limits as it until reaching acceptable fault levels.
The content of the invention
It is an object of the present invention to provide the method and apparatus for allowing the reconstruct of object wave, wherein eliminating Fu by hologram The Chong Die phenomenon for causing of the DC energy levels in the two-dimension spectrum that vertical leaf transformation is obtained and the first image energy level.
This target is realized by being related to the above, the method for further comprising the steps species：Generation is adapted to be Avoid the second coherent reference light beam with the interference of the first reference beam；Second reference beam is directed to into the first mirror, and will be by The light beam of first mirror reflection is directed to optical pickocff, wherein path of second reference beam from light source to sensor have with The different length of the length of the equivalent path of the first reference beam；In the two-dimension spectrum of the Fourier transform in spatial frequency domain Produce the conjugation of the second image energy level and the second image energy level；And replaced and DC energy levels by the appropriate section of the second image energy level The part of the first image energy level for overlapping.
The shortcoming of prior art is this approach avoid, because the part of the expression of the object wave Chong Die with the expression of DC energy levels Replaced by the appropriate section not with the expression of the object wave of DC group-overlaps.
In addition to above-mentioned method, the invention further relates to be used to prepare the dress of the digital hologram for representing object Put, the device includes：Light source, is adapted to be generation coherent measurement light beam and the first coherent reference light beam；Optical pickocff；First Mirror, extends under the angle different from pi/2 with its optical axis；Retainer, keeps object；Read and processing unit, be connected to optics Sensor, for reading optical pickocff and providing the digital signal for representing the interference figure for projecting on the optical sensor；Light Unit is led, is adapted to measuring beam from light source-guide to the object kept in retainer；For being reflected by the object Measuring beam be directed to optical pickocff；For by the first reference beam from light source-guide to the first mirror；And for will be by First reference beam of the first mirror reflection is directed to the optical pickocff so that produce interference figure on the optical sensor, Wherein the reading and processing unit are adapted to be：Process the digital signal to obtain digital hologram；Make the digital hologram experience Fourier transform in spatial frequency domain is obtaining the two dimension including DC energy levels, the first image energy level and the first conjugated image energy level Spectrum；And the spectrum experience filtering for making to obtain, to obtain the energy level for representing object, wherein the light source is adapted to be generation and is fitted With to avoid the second coherent reference light beam with the interference of the first reference beam, wherein the optical guide unit is adapted to be the second ginseng Examine light beam and be directed to the first mirror, and optical pickocff will be directed to by the light beam of the first mirror reflection, wherein the second reference beam Path from light source to sensor has the length different from the length of the equivalent path of the first reference beam, and the wherein reading It is adapted to be by the appropriate section of the second image energy level to replace the first image energy level with DC group-overlaps with processing unit Part.
The method that first preferred embodiment provides the species that above is referred to, wherein by the appropriate section of the second image energy level Replacement is carried out with the part of the first image energy level of DC group-overlaps by following steps：The numeral for making image represents experience Fu Vertical leaf transformation is entered in spatial frequency domain；The spatial frequency spectrum for making the image for obtaining experiences spatial frequency filtering so that two The expression of object wave is still suffered from；The expression for making two object waves experiences inverse Fourier transform in spatial frequency domain；So that object The expression experience of ripple applies two reference beams；Fourier transform is experienced in the expression for making the image for obtaining；By the phase of the second image Answer the spectra part of the overlap of the image of partial replacement first；And make the SPECTRAL REGION of the first image experience inverse Fourier transform.
Although not excluding the additive method for replacing energy level, above-mentioned optimal seeking method side provides carries out having for this replacement Efficacious prescriptions formula.
The device of species of the similar consideration to above is referred to is also valuable, and wherein the reading and processing unit are adapted It is that the first image energy with DC group-overlaps is replaced by the appropriate section of the second image energy level by procedure described above The part of level.
As described above, the reference beam of application claims first and second is not interfered.Exist and produce such light beam Several probabilities, but according to preferred embodiment, the first reference beam and the second reference beam are polarized mutually orthogonally (polarized).Cross-polarization provides one group of light beam, and two of which reference beam is not interfered, but wherein reference light Any one of beam is possible with the interference of measuring beam.
Although not excluding other implementations, this embodiment is preferably realized by the following method：Wherein first and Two reference beams are produced by identical light source and two of which reference beam experiences mutually orthogonal polarizer.
Identical advantage is obtained in following device, the wherein optical guide unit is included in the path of the first reference beam The first polarizer, the second polarizer in the path of the second reference beam, and wherein the first and second polarizings Device orthogonally polarizing.
In order to allow the interference figure and the first reference beam and the survey that produce between the second reference beam and measuring beam Interference figure between amount light beam is different, and in addition to avoiding the requirement for interfering, the first and second reference beams must have There are different characteristics
According to preferred embodiment, realize via the second mirror guiding second vertically extended with the axle of the second reference beam Reference beam.This embodiment additionally provides the device including the second mirror vertically extended with the axle of the second reference beam, the light Lead unit to be adapted to be via the second mirror second reference beam of guiding.
Although the invention provides for being replaced and DC by the appropriate section not with the second image energy level of DC group-overlaps The good solution of the part of the first image energy level of group-overlap, but the part for overlapping first mustn't be fully little being replaced Change.Specifically, it should be not more than whole half for representing of light beam.In order to realize this, further preferred embodiment is provided The mould of the substantial portion of the first image energy level is equal to the feature of the mould of the virtual part of the first image energy level.
According to the implementation in attractive structure, the optical guide unit is included with primary optic axis and the second optical axis Beam splitter, light source is located on primary optic axis, and at the side relative with light source side, optics is passed the reference mirror on primary optic axis Sensor be located at the second optical axis on, and retainer be adapted to be position the object against it is relative with Fibre Optical Sensor side on the second optical axis Side.
Claim before is related to the preparation of hologram.In order to enjoy all advantages of the present invention, the present invention is also provided The method that reconstruct represents the image of object.
Here, preferred embodiment provides the thing that reconstruct is represented by the digital hologram that the method by above is referred to is obtained The method of the image of body, wherein digital hologram experience the numeral of the plane wave as reference wave and represent, and digitally perform Reconstruct.
Another embodiment provides such method, wherein the image for representing object is digitally processed to obtain digital height Degree figure.
The present invention can be applied in optical coherence x-ray tomography art, according to corresponding method, the measuring beam It is adapted to be and at least partially penetrates into object and produce scattered beam, and wherein scattered beam and first and second in object Measuring beam combines to form interference figure on the optical sensor.
The method allows to collect the information from the upper strata of object.
In addition present invention could apply to interferometry.Thus in space-wise, measuring beam and first and second Reference beam is focused on object, and replaces the first image with DC group-overlaps in the appropriate section by the second image energy level During the part of energy level, omit to the expression of image and apply two reference waves.
This will be become more fully understood according to detailed description given below and only by illustrating the accompanying drawing for providing Bright above and other target, feature and advantage, therefore they will not be considered as to limit the present invention.
Description of the drawings
Fig. 1 is the figure of the prior art optical arrangement for illustrating the outer digital holography of axle；
Fig. 2 is the flow chart of the restructuring procedure of the outer digital holography of typical axle；
Fig. 3 is the figure of the optical arrangement for illustrating the outer DH of axle of the invention；
Fig. 4 is the figure according to Fig. 3 with low-coherence light source；
Fig. 5 A and 5B are two figures of the spatial frequency content that the hologram according to prior art and the present invention is shown respectively；
Fig. 6 is the flow chart according to Fig. 2, wherein having applied two reference waves；
Fig. 7 A and 7B are the 2D intensity images and 3D height maps of electronic circuit image；
Fig. 8 A are the digital holograms of the outer DH of prior art axle；
Fig. 8 B are the spatial spectral of the hologram drawn in Fig. 8 A, and wherein rectangle indicates the quadrant for including object wave；
Fig. 9 is the spatial spectral of object wave, wherein the spatial frequency content of dashed circle indicant bulk wave；
Figure 10 A are the 2D intensity images of reconstruct；
Figure 10 B are the 3D height maps of reconstruct；
Figure 11 A are the digital holograms of the outer DH of axle of the invention；
Figure 11 B are the spatial spectral of the hologram drawn in Figure 11 A；
Figure 12 is the spatial spectral of the object wave extracted according to the present invention；
Figure 13 A are the 2D intensity images of reconstruct of the invention；
Figure 13 B are the 3D height maps of reconstruct of the invention；And
Figure 14 is to draw the figure that the feature of the present invention is applied to x-ray tomography art.
Specific embodiment
Fig. 1 discloses the prior art arrangement of the outer digital holography of axle, wherein slave phase dry bulk wave (O) and phase trepang The interference examined between ripple (R) obtains hologram.Then, two-dimentional (2D) intensity distributions (IH) can be expressed as：
IH(x, y)=(R+O) (R*+O*)=| R |2+|O|2+R*O+RO* (1)
Wherein R*And O*Represent the complex conjugate of two ripples.
After record hologram, can be obtained by irradiating hologram with reconstruct ripple (reconstruction wave) U The ripple (reconstructed wave) that must be reconstructed is (ψ) as follows：
ψ=IHU=| R |2U+|O|2U+R*OU+RO*U (2)
Front two energy level of equation (2) forms the zeroth order of diffraction, sometimes referred to as DC energy levels.Third and fourth energy level is by interfering energy Level is produced, and they produce two conjugation or paired image of object.Three-level (R*OU) produce and be located at object (object Plane) initial position virtual image, four-level (RO*U) produce the opposite side positioned at hologram (in the plane of delineation) Real image.
If irradiating hologram to be reconstructed by the copy (U=R) with reference wave, the 3rd energy of equation (2) Level is changed into the copy of object wave and is multiplied by referenced strength (| R |2O).If conversely, U=R*, then four-level is conjugation object wave Copy be multiplied by referenced strength (| R |2O*)。
For the reconstruct of object wave.Three-level should be only extracted from original hologram, such as shown in equation (2).Outside axle In the case of DH, the two-dimension spectrum of the hologram in spatial frequency domain can be obtained by Fourier transform so that can be easy Extracted because by spatial modulation, the different energy levels of interference produce the effect of good separation.It is then possible to such as Several technical filters of bandpass filtering or nonlinear filtering fall undesirable energy level of equation (2), and can only extract simultaneously Obtain three-level.
Fig. 2 illustrates the restructuring procedure of the outer DH of typical axle.
But, as it was previously stated, the object wave extracted from hologram still has by between DC energy levels and object wave energy level Some noises that overlapping region causes.Even, non-linear filtering method may be subject to its operating condition in actual applications Limit.
In the present invention, the effective space filtering technology of novelty for extracting object wave in the outer DH of axle is given.Its It is based in single image and obtain simultaneously two digital holograms, they can be separated by unique spatial modulation. In other words, using two reference wave (R with different spaces modulation direction1And R2) recording digital hologram, this and typical case The outer DH of typical shaft only using a reference wave is contrary on ground.
So as to each reference wave can produce each interference with object wave.It is noted that the interference between two reference waves During this image comprising two holograies should not be included in.For example, this can be by using the light of cross-polarization in practice Or realized using low coherence source, as shown in Figure 3 and Figure 4.
Fig. 3 is disclosed and the basically identical configuration of configuration shown in Fig. 1, but wherein the second beam splitter 15 is located at the Between one object lens 4 and reference mirror 5.The second reference mirror 16 is further provided, it is optically connected to the second beam splitter 15. This configuration allows not only to process the reference beam 10 of measuring beam 11 and first, and processes the second reference beam 12.
Here, the second reference beam is directed into the second mirror 16 via the second beam splitter 15, it is allowed to all three light Beam 10,11 and 12 runs into imageing sensor 7.This also allows to produce two interference figures, i.e. measuring beam and the first reference beam Between the first interference figure and the second interference figure between measuring beam and the second reference beam.In order to forbid appearance two Interfering between individual reference beam 10,12, is preferably for example separated by using polarization beam splitter as the second light beam Device 15 and the two light beams is orthogonally polarized.
Fig. 4 draws the structure of one embodiment, wherein avoiding interfering between reference beam using other features. In this embodiment, light source is low coherence light source 21.Can be by defining come the low coherence light of light source since then (definition) interference range is limited.The structure of this embodiment drawn in Fig. 4 is equal to the structure of preceding embodiment, but The position of wherein the second reference mirror 16 be adjusted with avoid interference between two reference beams and-certainly-use Low coherence light source.
As a result, comprising the image (I of two holograies in the method2H) can be expressed as：
I2H(x, y)=| R1|2+|O|2+|R2|2+|O|2+R1 *O+R1O*+R2 *O+R2O* (3)
Similar to equation (2), the zeroth order diffraction (or DC energy levels) in the front four-level intenest space frequency domain of equation (3). 5th and the 6th energy level is R1Interference energy level, its spatial frequency with regard to the image in spatial frequency domain centrosymmetry be distributed. On the other hand, the 7th and the 8th energy level is R2Interference energy level, its spatial frequency is also symmetrical.In the case, due to R1 Modulate with the different spaces of R2, this four are interfered energy level to be spatially separated in spatial frequency domain.It is preferred that in this method Each energy level is located in each quadrant in the domain at the inclination angle that have adjusted reference mirror, and within hardware this is not what is special Work.
In fact, the main difficulty that object wave is extracted in the outer DH of typical axle is being by the DC energy levels in spatial frequency domain And interfere what the overlapping region between energy level (object wave and its conjugation) caused, as shown in Figure 5A.
But, in the present invention, the overlapping region between DC energy levels and object wave in the first hologram can be with second The Non-overlapping Domain of the object wave in hologram is replaced, because image includes two holographies that wherein have recorded same object ripple Figure.For example, R1 *Overlapping region (object wave (the R of O1 *O) the left lower quadrant of frequency content) R can be used2 *The Non-overlapping Domain of O is replaced Change, as shown in Figure 5 B.This be based on the fact that：The spatial modulation frequency of reference wave may be located in the diagonal axis in the domain, And the major part of overlapping region is placed in a quadrant of the spatial frequency content of the object wave between DC energy levels and object wave In.
In practice, each the object after ripple is added to each bandpass filtering can will be being reconstructed (with each reference wave identical) This operation is carried out after ripple.In other words, it is possible to use two reference waves obtain respectively two object waves.In theory they should It is identical, but it is slightly different due to overlapping region.According to the two object waves, then, an object wave in overlapping region Spatial frequency component by with another object wave in Non-overlapping Domain spatial frequency component replace.In most of the cases, The method can provide more preferable amplitude and phase information, because except the little spatial frequency modulation of reference wave or with high-altitude Between frequency component high degree of rigidity (stiff) object outside, overlapping region is a quadrant of the spatial frequency content of object wave.
Even if in the worst case, the method can also reduce more overlay errors than additive method.So as to outside axle Another reference wave allows to provide the space frequency of second hologram in the second hologram of other object wave used in DH Non-overlapping Domain in rate domain to replace the first hologram in DC energy levels and object wave between overlapping region.
After the accurate object wave that the filtering method new using this obtains in holographic plan, in number based on classification Diffraction theory, the ripple returns to object wave plane from hologram plane propagation.By adopting Fresnel approximation, can be flat from hologram Object wave (ψ in faceH) calculate the object wave (ψ for reconstructingO) be：
Wherein λ is wavelength, and d is the distance between holographic plan and object plane.(xO,yO) and (xH,yH) refer to thing respectively The two-dimensional coordinate of body plane and holographic plan.
2-D Fourier transforms in F { } representation space domain.A is the Arbitrary Digit determined by the amplitude of reference wave and reconstruct ripple Word.According to the ripple (ψ for obtainingO), the amplitude and phase image of object can be split, finally obtain 3D surfaces from phase image high Degree figure.
Fig. 6 is illustrated in the present invention using two whole process with reference to the accurate object wave of reconstructed wave.In order to confirm this The effectiveness of invention, is entered using the typical space filtering based on bandpass filtering and using the new filtering technique of two reference waves The simulation of the outer DH of row axle.In order to produce digital hologram, using electronic circuit image (181 × 181 pictures as shown in figs. 7 a-b Element).Fig. 7 A illustrate the 2D intensity images of circuit, and Fig. 7 B provide the 3D height maps of circuit.Hypothesis maximum height is 100nm to avoid Fuzzy problem.The distance between object plane and holographic plan are 2mm.
In the outer DH of typical axle, only one reference wave be used to interfere, and can obtain number on holographic plan Word hologram, as shown in Figure 8 A.In the hologram, with inclined reference wave interferometric modulator energy level.Then, using 2D Fouriers In the spatial frequency domain of leaf transformation, digital hologram can split DC energy levels, object wave and its conjugation, as shown in Figure 8 B.Including Object wave (R*O quadrant) is left lower quadrant.
In order to object wave, including the quadrant of object wave are extracted from the hologram only by bandpass filtering, and and reference wave Identical reconstruct ripple is applied to the energy level after filtering to remove spatial modulation frequency.Fig. 9 illustrates the spatial spectral of object wave.Such as Shown in Fig. 9, in the filtering rear region outside dotted line circle DC energy levels are with the addition of, it means that most of spatial frequency of object wave Content.Further bandpass filtering can apply to this spectrum to remove DC energy levels, but, as it was previously stated, which limit object The available spectrum of ripple, and generally need manpower intervention to select desired level.
After filtering to object wave, last step is numerically to propagate object wave using equation (4).In the result, 2D intensity images and 3D height maps are reconstructed, as illustrated in figs. 10 a and 10b.It is noted that the edge of image is by apodization (apodized) Affected with removing the diffraction caused by the edge of image during digital communication.Figure 10 A and 10B are shown mainly due to remaining Some pseudomorphisms in the image of the reconstruct that DC energy levels cause.
On the other hand, the image for obtaining from the outer DH of new axle of the present invention includes two holograies, and it refers to by different empty Between modulate two diacritic interference, as shown in Figure 11 A.
In spatial frequency domain, there are two object wave energy level (R1 *O and R2 *O) and its conjugation (R1O*And R2O*) energy level.It is left Lower quadrant is included using the first reference wave (R1 *O object wave), left upper quadrant is included using the second reference wave (R2 *O object) Ripple.Then, after by each reference wave application for reconstruct ripple, using two object wave spectrums, R1 *In O including left lower quadrant Upper part DC energy levels region by with R2 *Do not wrap the upper partial replacement of the left upper quadrant in O, the upper part of the left upper quadrant Include DC energy levels.Because eliminating DC energy levels using this process, the spatial frequency of the object wave for obtaining is not by the shadow of DC energy levels Ring, as shown in figure 12.
Figure 13 illustrates the 2D reconstructed after the digital communication of the object wave that application is extracted by the new technology of the present invention Intensity image and 3D height maps.With comparing with the image of the traditional method reconstruct shown in 10B by Figure 10 A, image tool is confirmed There is better quality and it does not include any pseudomorphism occurred in Figure 10 A and 10B.
Finally, Figure 14 is depicted and wherein the feature of the present invention is applied to into the situation of x-ray tomography art.In this background In x-ray tomography art in, understand the research to the upper strata of object.This wording " x-ray tomography art " have with This wording it is more common using different implications, to indicate wherein by transmitted radiation inspection body and wherein body is relative In the process that transmitted radiation source and its detector rotate.
In the present invention using with penetrate upper strata up to a certain degree and experience scattering in upper strata this characteristic light Beam.Scattered beam is further subjected to and the reflected beams identical process in embodiment before.
It will be clear that, it is possible to the various change of embodiments disclosed above within the scope of the appended claims.
Procedure described above of the present invention can be by the calculating with CPU, ROM and the RAM for performing computer-readable program Machine is carried out.
Using any type of nonvolatile computer-readable medium storage program and computer can be provided it to.It is non-temporary Computer-chronograph computer-readable recording medium includes any type of actual storage medium.The example of nonvolatile computer-readable medium is deposited including magnetic Storage media (such as floppy disk, tape, hard disk drive etc.), light magnetic storage medium (such as magneto-optic disk), (compact disk is read-only for CD-ROM Memorizer), CD-R (compact disk can record), CDR/W (compact disk is writeable) and semiconductor memory (such as mask ROM, PROM (programming ROM), EPROM (erasable PROM), flash ROM, RAM (random access memory) etc.).Any type can be used Nonvolatile computer-readable medium program is supplied to into computer.The example of nonvolatile computer-readable medium includes telecommunications Number, optical signal and electromagnetic wave.Temporarily computer-readable medium can be via wire communication line (such as electric wire and optical fiber) or wireless Program is supplied to computer by order wire.
In the present invention of such description, will be apparent from embodiments of the invention can change in numerous ways root.Such change Change is not to be regarded as a departure from the spirit and scope of the invention, and will be apparent to one skilled in the art all such Modification intention is included in the range of following claims.
The application is the European Patent Application No. 11179946.6 based on the submission on the 2nd of September in 2011, and requires its priority Rights and interests, it is open by reference to being all herein incorporated.

Claims (12)

1. a kind of method of the digital hologram for preparing the image for representing object, the method comprises the following steps：
Produce measuring beam and the first reference beam；
Object is irradiated by measuring beam and the measuring beam being reflected by the object is directed to into optical pickocff；
First reference beam is directed to the first reference mirror for reflecting the first reference beam with angle of inclination, and will by this First reference beam of one reference mirror reflection is directed to the optical pickocff so that the measuring beam that is reflected by the object and by institute The first reference beam for stating the reflection of the first reference mirror produces together the first interference figure on the optical pickocff；
The second reference beam is produced, it is adapted to be and avoids interfering with first reference beam；
Second reference beam is directed to into the second reference mirror, and will be drawn by the second reference beam of the second reference mirror reflection Lead the optical pickocff so that the measuring beam reflected by the object and the second ginseng reflected by second reference mirror Examine light beam and produce the second interference figure on the optical pickocff together, wherein the second reference beam is from light source to the optics The path of sensor has from the first reference beam from the light source to the length that the path of the optical pickocff is different；
Optical pickocff and providing is provided and represents the first interference figure for producing on the optical sensor and the second interference figure Digital signal；
Process the digital signal to obtain digital hologram；
Make the Fourier transform in digital hologram experience spatial frequency domain with obtain including DC energy levels, the first image energy level, First conjugated image energy level, the second image energy level, the two-dimension spectrum of the second conjugated image energy level, wherein from the first interference figure The first image energy level and the first conjugated image energy level are drawn, the second image energy level and the second conjugation are drawn from the second interference figure Image energy level；
The two-dimension spectrum for obtaining is set to experience filtering to obtain described first image energy level and the second image energy level；
By in partial replacement the first image energy level of the second image energy level by the part of DC group-overlaps, the second image energy level The part corresponding in the first image energy level by DC group-overlaps and not by the part of DC group-overlaps.
2. method according to claim 1, wherein the first reference beam and the mutually orthogonal polarization of the second reference beam.
3. method according to claim 2, wherein the first reference beam and the second reference beam produced by identical light source and They experience mutually orthogonal polarizer.
4. method according to claim 1, wherein the second reference mirror vertically extends with the axle of the second reference beam.
5. method according to claim 1, wherein the mould of the substantial portion of the first image energy level is equal to the void of the first image energy level Intend the mould of part.
6. a kind of for reconstructing the image of object represented by the digital hologram obtained by method according to claim 1 Method, the wherein digital hologram experience the numeral of the plane wave as reference wave and represent, and digitally perform the reconstruct.
7. method according to claim 6, wherein the image for representing object is digitally processed to obtain digital elevation model.
8. method according to claim 1, wherein the method is applied in x-ray tomography art,
The measuring beam is adapted to be and at least partially penetrates into object and scattered beam is produced in object, and
Both scattered beam and first and second measuring beams combine to form interference figure on the optical sensor.
9. a kind of device for preparing the digital hologram for representing object, the device includes：
Light source, is adapted to be generation measuring beam and the first reference beam；
Optical pickocff；
First reference mirror；
Second reference mirror；
Retainer, keeps object；
Read and processing unit, be connected to optical pickocff, for reading optical pickocff and providing expression optical sensing is incident upon The digital signal of the interference figure on device；
Optical guide unit, is adapted to：
First reference beam and measurement light will be separated into from the light including the first reference beam and measuring beam of light source Beam；
By measuring beam from light source-guide to the object kept in retainer；
The measuring beam being reflected by the object is directed to into optical pickocff；
First reference beam is directed to the first reference mirror for reflecting the first reference beam with angle of inclination；And
The optical pickocff will be directed to by the first reference beam of the first reference mirror reflection so that the measurement being reflected by the object Light beam and by first reference mirror reflect the first reference beam produce the first interferogram on the optical pickocff together Case；
The second reference beam is produced, it is adapted to be and avoids interfering with first reference beam；
Second reference beam is directed to into the second reference mirror,
The optical pickocff will be directed to by the second reference beam of the second reference mirror reflection so that reflected by the object Measuring beam and by second reference mirror reflect the second reference beam produce second on the optical pickocff together Interference figure, wherein the second reference beam from the light source to the path of the optical pickocff have with the first reference beam from The light source is to the different length in the path of the optical pickocff；
Wherein the reading and processing unit are adapted to be：
Process the digital signal to obtain digital hologram；
Make the Fourier transform in digital hologram experience spatial frequency domain with obtain including DC energy levels, the first image energy level, First conjugated image energy level, the second image energy level, the two-dimension spectrum of the second conjugated image energy level, wherein from the first interference figure The first image energy level and the first conjugated image energy level are drawn, the second image energy level and the second conjugation are drawn from the second interference figure Image energy level；
The two-dimension spectrum for obtaining is set to experience filtering to obtain the first image energy level and the second image energy level；
By in partial replacement the first image energy level of the second image energy level by the part of DC group-overlaps, the second image energy level The part corresponding in the first image energy level by DC group-overlaps and not by the part of DC group-overlaps.
10. what device according to claim 9, the wherein optical guide unit were included in the path of the first reference beam first is polarized Shake device, the second polarizer in the path of the second reference beam, and the orthogonally polarizing of the first and second polarizers.
11. devices according to claim 9, wherein the second reference mirror vertically extends with the axle of the second reference beam.
12. devices according to claim 9, the wherein optical guide unit include that the light beam with primary optic axis and the second optical axis is separated Device, the light source is located on primary optic axis,
The first reference mirror on primary optic axis in the side relative with light source side,
Optical pickocff is located on the second optical axis, and
Retainer is adapted to be and positions the object against side relative with Fibre Optical Sensor side on the second optical axis.
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CN110296666B (en) * 2018-03-23 2021-04-20 泓邦科技有限公司 Three-dimensional measuring device

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